Acmella oleracea extract increases collagen content and organization in partially transected tendons

Acmella oleracea contains spilanthol as the main active compound, which possesses analgesic and anti-inflammatory effects that can favor tendon reorganization. To analyze the effect of A. oleracea on the content and organization of collagen in injured tendons, the calcaneal tendon of male Lewis rats was partially transected and treated at the site of injury with a topical application of 20% A. oleracea ointment (AO group) or with the ointment base without the plant extract (B group). The animals were euthanized 21 days after partial transection. Higher collagen concentration was observed in the AO group than in the B group, and morphological analysis using polarization microscopy showed higher birefringence in the AO group than in the B group, indicating higher collagen organization. No difference was observed in the number of fibroblasts, blood vessels, proteoglycan distribution, and maximum load between the B and AO groups. In conclusion, topical application of 20% A. oleracea ointment increased the molecular organization and content of collagen, thus indicating a potential application in tendon repair. Studies on the later phases of the tendon healing process are necessary to demonstrate the possible biomechanical changes after the application of A. oleracea ointment.